Communicating between ships at sea was done by flags, an International Code signals was published in England in 1857.
- International Code of Signals – Wikipedia
The International Code of Signals (ICS) is an international system of signals and codes for use by vessels to communicate important messages regarding safety of navigation and related matters. Signals can be sent by flaghoist, signal lamp (“blinker”), flag semaphore, radiotelegraphy, and radiotelephony.
- International maritime signal flags – Wikipedia
International maritime signal flags refers to various flags used to communicate with ships. The principal system of flags and associated codes is the International Code of Signals.
- International Code of Signals (Overview) – Flagspot.net
The International Code of Signals was first drafted in 1855 by the British Board of Trade and subsequently published in 1857 as a means of maritime communications. The original publication showed 17,000 signals using 18 flags, part of which was specific to the United Kingdom and another part that contained universal signals to be used by all nations.
- Brief history of the International Code of Signals. – Naval Marine Archive
The first International Code was drafted in 1855 by a Committee set up by the British Board of Trade. It contained 70,000 signals, it used eighteen flags and it was published by the British Board of Trade in 1857 in two parts; the first containing universal and international signals and the second British signals only.